en گروه مکانیکی و شکل دادن Mechanical Performance and Formability of Materials Research Paper Research Paper <span style="font-size:12pt"><span style="line-height:200%"><span new="" roman="" style="font-family:" times=""><span style="font-size:11.0pt"><span style="background:lime"><span style="line-height:200%"><span style="background-color:#ecf0f1;">This work presents a comprehensive investigation of the high cycle fatigue behavior of Haynes 25 cobalt-based superalloy and its welds produced by pulsed continuous-wave (CW) laser welding.</span></span></span></span><span style="font-size:11.0pt"><span style="line-height:200%"><span style="background-color:#ecf0f1;"> The alloy, manufactured through vacuum induction melting and electroslag remelting followed by rolling and annealing, exhibited a yield strength of 650 MPa, an ultimate tensile strength of 1050 MPa, and an outstanding elongation of 57% at room temperature. The fatigue limit was determined by </span><span style="background:lime"><span style="background-color:#ecf0f1;">test method</span></span><span style="background-color:#ecf0f1;"> as 200 MPa for lifetimes exceeding 10⁸ cycles, highlighting its excellent resistance to cyclic loading. For the weld zone, fabricated under optimized pulsed CW laser parameters, the yield and ultimate tensile strengths were 660 MPa and 965 MPa, respectively, with a fatigue limit of 175 MPa. Advanced microstructural analyses using OM, SEM, EBSD, and XRD revealed an austenitic FCC matrix with carbide precipitates, predominantly (W, Cr)₇C₃ and M₆C, decorating both the matrix and grain boundaries. Fatigue crack initiation in the base metal was associated with carbide clusters near the surface, while in the weld zone it was strongly linked to near-surface gas porosity defects. These findings not only establish fundamental fatigue benchmarks for Haynes 25 but also provide the first direct insights into the microstructural origins of fatigue damage in its laser-welded joints, thereby addressing a critical knowledge gap for its deployment in high-temperature and cyclic-loading environments.</span></span></span></span></span></span> Haynes 25,Cobalt based,Fatigue,Strength,Fractography 72 85 http://ijmse.iust.ac.ir/browse.php?a_code=A-10-5431-2&slc_lang=en&sid=1 Mahdi Behjati mahdi.behjati@ut.ac.ir 1800319475328460021851 1800319475328460021851 No Space transportation research institute, Iranian Space Research Center, Tehran, Iran Seyed Ali Asghar akbari Mousavi akbarimusavi@ut.ac.ir 1800319475328460021852 1800319475328460021852 No School of Metallurgy and Materials Engineering, College of Engineering, University of Tehran, Tehran, Iran Yaser Vahidshad y.vahidshad@isrc.ac.ir 1800319475328460021850 1800319475328460021850 Yes Space transportation research institute, Iranian Space Research Center, Tehran, Iran